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A basket of overripe fruit magically attracts vinegar flies. As soon as they land, the insects deposit tiny droppings of droppings to make their fellow species aware of the feeding site. This is what scientists at the Max Planck Institute for Chemical Ecology in Jena found out.
For the study, various experiments were carried out with two to five day old vinegar flies (Drosophila melanogaster). Among other things, the scientists set up traps with different fragrances and counted the flies baited in this way. In a further experiment, they determined how attractive or deterrent a fragrance is. In addition, individual animals were placed in a glass tube into which various gases were introduced. A fragrance was considered attractive if the fly moved against the wind, i.e. in the direction of the fragrance source. With the help of a chemical analysis, the scientists investigated which substances in the faeces are so attractive to the flies.
Vinegar flies find food sources through the scent of overripe fruit.
The fruit is not only used for food intake, but is also a place to find a partner and lay eggs after mating. The evaluation of the data has shown that the faeces are an important communication tool. The excretions contain sexual fragrances, which differ depending on the type and gender. The volatile substances attract fellow species, as the test in the glass tube confirmed: the flies always smelled out of their faeces in the direction of the fragrance source. Even the smallest quantities drastically increase the attractiveness of the fruit. At the same time, the flies eat more food if there are piles of droppings on the fruit.
If a particularly large number of flies seek fruit, more eggs are laid. The hatching fly larvae can benefit from the presence of other larvae. Presumably, it will make it easier to eat if the fruit is already "pre-digested" by the microorganisms in the faeces. Future studies will clarify that. It would also be interesting to see whether the scent that takes getting used to also influences the choice of partner, the courtship behavior and the oviposition of the flies. It remains open whether the results can be transferred to related species such as the cherry vinegar fly. This important pest in fruit and wine growing primarily affects young fruits. (Heike Kreutz, aid)